Computing devices and other similar devices implemented to send and/or receive data can be interconnected in a wired network or a wireless network to allow the data to be communicated between the devices. Wired networks, such as wide area networks (WANs) and local area networks (LANs) for example, tend to have a high bandwidth and can therefore be configured to communicate digital data at high data rates. One obvious drawback to wired networks is that the range of movement of a device is constrained since the device needs to be physically connected to the network for data exchange. For example, a user of a portable computing device will need to remain near to a wired network junction to maintain a connection to the wired network.
An alternative to wired networks is a wireless network that is configured to support similar data communications but in a more accommodating manner. For example, the user of the portable computing device can move around within a region that is supported by the wireless network without having to be physically connected to the network. A limitation of conventional wireless networks, however, is their relatively low bandwidth which results in a much slower exchange of data than a wired network. Wireless networks will become more popular as data exchange rates are improved and as coverage areas supported by a wireless network are expanded.
Rectangular waveguides can be implemented in data transmission systems as antennas and as low loss transmission lines to communicate data from one device to another in the form of a propagated electromagnetic field. A rectangular waveguide has a cutoff frequency (or wavelength) that is determined by the physical size of the device. The width of the waveguide determines the cutoff frequency (λco) which can be represented by λco=2a, where “a” is the width of the waveguide. Any frequency above the cutoff frequency is propagated. Typically, the recommended operating frequency range of a rectangular waveguide is approximately twenty-five percent (25%) above the cutoff frequency and five percent (5%) below the frequency where λ=a. Operating above this frequency is undesirable because higher order modes can occur which interfere with the fundamental mode causing signal distortion and increased signal attenuation.
An additional property related to the cutoff wavelength λco of the waveguide is the guide wavelength λg which is the wavelength as determined within the waveguide. The guide wavelength λg is related to the cutoff wavelength λco by the equation:       λ    g    2    =                    λ        2            /      1        -                  (                  λ          /                      λ            co                          )            2      As the operating wavelength λ approaches the cutoff frequency λco, the guide wavelength λg gets larger (the guide wavelength λg is always larger than the operating wavelength λ).
A rectangular waveguide that is implemented as an antenna element can be formed with slots in a wall of the waveguide for electromagnetic signal transmission. The slots are typically spaced λg/2 apart in the antenna element wall. To keep the slot spacing operating frequency reasonably close to that of free space (i.e., λ/2), and to keep the length of the antenna element as short as possible, the operating frequency λ must be well above the cutoff frequency λco. It is difficult to design and construct a rectangular waveguide as an antenna element that can be combined with multiple antenna elements to form an antenna array that is small enough to be physically manageable while having a useful operating frequency. Further, for an array of slotted waveguide antenna elements that are positioned together to form the antenna array, the ideal spacing of λ/2 between waveguide antenna element centers is not achievable.